C.I. Solvent Black 3 is an oil-soluble diazo dye stuff which is prepared by art-known methods. For example, it may be prepared by diazotizing aniline with naphthylamine followed by coupling with 2,2'-dimethyl-2,3-dihydropyrimidine. C.I. Solvent Black 3 is commercially available as Sudan Deep Black BB (BASF A. G.), Neptune Black (BASF A. G.), Oil Black BT (National Aniline Div. Alliee Chemical & Dye Corp.), Seles Black (Farbenfabriken Bayer A. G.) and Oil Black HBB (Orient Chemical Industries, Ltd.).
C.I. Solvent Black 3, however, contains unreacted components, by-products and impurities from reactants. These must be removed therefrom, in order for the end products, e.g. ink and the like, to be characterized with good properties.
Recently, safety to the human body has become more significant in the field of recording materials. In view of this point, non toxic or less toxic coloring agents are desired. Conventional C.I. Solvent Black 3 has a possibility of variation to microorganism, which is believed due to the impurities.